FIGURE 1.

Siglec-1 is expressed on mouse macrophages in an IFNα-responsive manner and supports MLV trans-infection. A,ANA-1 cells or BMDM were stimulated with mouse IFNα (500 units/ml) for 48 h or left untreated. Mechanically detached cells were stained using a phycoerythrin-conjugated anti-mSiglec-1 mAb or an isotype control mAb and analyzed by flow cytometry. Shown are untreated cells (black lines) or IFNα-treated cells (shaded histograms) stained for mSiglec-1 and untreated cells (dotted line) stained with the isotype mAb. B, each of the indicated cell types was infected with MLV-GFP (m.o.i. 0.1) and 2 days later analyzed for GFP expression, indicative of productive infection, by flow cytometry. C, experimental setup for assessment of MLV trans-infection. 1, addition of MLV particles to macrophages; 2, addition of target lymphocytes to macrophage culture. D, BMDM or ANA-1 cells were stimulated with mouse IFNα (500 units/ml) for 48 h or left untreated. Cells were preincubated with an anti-Siglec-1 mAb or an isotype control mAb at 4 °C, exposed to MLV-GFP (m.o.i. 0.1) for 4 h at 37 °C, and washed three times in PBS. S1A.TB cells were then added in a 1:1 ratio to the virus-pulsed macrophage cultures for 48 h and then analyzed for GFP expression by flow cytometry. Data are expressed as the arithmetic means ± S.D. of triplicate samples from one mouse and are representative of at least two experiments each performed using 2–3 mice.